Silver-beryllium oxide catalyst and method for making same



.l atented july 29, 1 952 S ILVEREBE-BYLEIUM OXIDE'YQATYALYST nn I ME OD on MAKINGSAME H GeorgeW, Sears; J r., and Wallace 'W- Thompson,

Wilmington,- Del., assignors to E. IrduPont fle -Nemurs &-Company, Wilmington; Del.,:a corporation-of Delaware ,NoDrawing. Application'Novemb er lzglg9 1 Serial,No.125,' 917 Silver catalysts so prepared are claimeidin, the

application. The silverzheryllium, Weight ratios employed were ,setout broadly asv 10 l to 15.000 1, morepreferably as 100:1.to 150,011. v

The activity of the silver:beryllium oxide ,catalyst compositions of the (earlier application (increases as the beryllium ,content isfincreased so that catalytic materials vobtainedfby. the coprecipitation procedure, containing.silvera beryllium weightratios of ,say 551 to 150.: 1,,are considerably more. activehatalystsifor ethylene oxidation than are .those containing larger amounts; of, silver in the coprecipitate.

.Unfortunately, ,prior to the present invention, the user of silver-beryllium oxide .coprecipitate. mixtures highin berylliumoxide (i. .e. AgzBe=5 1 to, .150: 1) a has not beam-entirely, satisfactory in the fluid-flow :processes im the oxidation of ethylene. to ethylene oxide. Thisisbecause such catalytic, materials.- exhibit. relatively little .cohesion ,or adhesion. Their exceptional activity is rapidly} lostin fluidflow operations because the silver?beryllium oxide coprecipitate mixture disintegrates and the effective catalytic ,properties of the mixture aredestroyed.

We'havenow discovered a methodu'for modifying'. the high beryllium ,oxide contain n rcatalytic materials ,of the previous. .inventi on .,toobtain .a catalyst which. retains, the high activity of those catalytic mixtures and is at the same time ire-i. sistant to disintegration,,thus having long catalyst rlife. i

1 .The catalyst compositions-v of ,thepresent-invention contain as an active catalytic material a silver-beryllium oxide mixture obtained as follows: A reducible oxygen-containing compound of, silver and aqcorresponding compound of .beryllium; are 'coprecipitated in 'a silverzberyllium weight ratio'o'f 5 1 to ;1-50:1 from a ,solution of a silver compound and a beryllium compound;

3 Claims. (01. 2521475) The .coprecipitate is intimately cmixed :with, ,:a separatelyprepared reducible oxygenecontaini-ng compound of silver. In the mixing,,;the;separately prepared silver .compound'eis,addediin amount corresponding to :atJJeast 25 .parts'gby weight-of silver for eachpart by weight 10-1 beryl-1 lium in the coprecipitate andthere ;is the. addi tional limitation that. the separately prepared silver compound beadded in J amountsufficient to give a resulting; mixture i in which the silver: beryllium weight-ratio is in :the range of .110'021 to 500 i l. The intimate mixture: is reduced. toira mixture of silver -and beryllium oxideijithen the reduced mixture-isheated ata temperature. or 3-50 to 600 C. for 3-to'10hours. I

I The term catalyst composition is usedfherein to refer to the total solid -mi-xture withwhich gaseous reactants" are contacted to -eiiect'- the. catalytic reaction. Thus gthe --t erm includese-not only the silver-beryllium;oxide;activecatalytic material but also all othermaterials inthe solid mixture such as carriers, supports;- diluents, pro-'- moters and' conditioning agents.

The expression reducible oxygcni-contaim g compound of silver refers to 'inorganic or 01 ganic silver compounds from which} metallic silver may be obtained by reducing either thermally or chemically. Such-compoundsinclude silver oxide; silver carbonate, silver nitrate and such organic 4 compounds as the silver salts -o'f carboxylic; acids-such as formic, acetic, "propionie, butyric,-isobutyric,--valeric, oxalic malic, malonic', lactic, andmaleicacids. Theter'm correspond ing compound of beryllium" reiers tosimilar'beryllium compounds such as'jberyllium hydroxide, beryllium carbonate; beryllium nitrate, "and or ganic beryllium compounds sucheas' the formate, acetate, propionate, oxalate and maleate-"- y 'In preparing. the silver -beryllium oxide active catalytic materials, a solution" containing f both a silversalt and a beryllium salt is'fir'st pr pared; as, for :examplefby dissolving Suve mtrateaaa beryllium nitrate in water. I Che-silver"a-ridfbr}yllium are coprecip'itated fromathe" solutio'n'astheir: corresponding water insoluble eases-cameras;- ide's,'- carbonates or carboxylic *a ci'd salts by ad'dition of an appropriate reagent: ipi ma -ash *bep einqb anqalkali "metalf beryllate, as by eac't g m i ra e. w hi sees ,alk ijmet' ll-hr r than addi 1-t 1ka1i. metal"Mi ime er silver nitrate'fs'olution to 'coprecip i-tate' the met-$1.15 s the r xid sg rhrqr i. B ry m.' sn e minor but relatively high amount. The *si;l

The separately prepared the silver compound which has been precipitated with the beryllium compound.

The separately prepared reducible silver compound is mixed With the coprecipitate. There are two limitations on the amount of separately prepared silver compound used in this mixing step. First, the amount added must as a minimum correspond to at least 25 parts by weight of silver for each part by weight of beryllium in the coprecipitate. Secondly, the amount added must be sufficient to give a resulting mixture having a silver beryllium weight ratio which is in the range of 100:1 to 500:1. Thus, for example, if the coprecipitate has a Ag:Be weight ratio of 150:1, then the separately prepared silver compound is added in amount corresponding to at least 25 parts by weight of silver for each part of beryllium in the coprecipitate, thus giving a resulting intimate mixture having a minimum Ag:Be weight ratio of 175:1. However, the separately prepared silver compound should not be added to the coprecipitate in an amount which the Ag:Be ratio was in the range of 100: 1 to 500: 1.

,The intimate mixture of separately prepared reducible silver compound with the coprecipitate may be attained in any suitable manner. Thus the two ingredients may be vigorously agitated in thepresence of sufficient liquid to form a paste. Preferably a freshly precipitated reducible oxygen-containing compound of silver is thoroughly mixed with a freshly prepared coprecipitate of reducible oxygen-containing compounds of silver and beryllium in the presence of suflicient water to, give a paste or heavy suspension of thesolids. The intimate mixture of the coprecipitate an theseparately prepared reducible. silver compound is then reduced, according tomethods heretofore known in the art for reducing silver compounds to give metallic silver catalysts, as by heating or chemically by treating with reducing gases such as ethylene, hydrogen or carbon monoxide to give a metallic silver-beryllium oxide mixture. Prior to this step, the mixture may be admixed with a suitable support or carrier.

Following the reduction step, the silver-beryllium oxide mixture is then heated to effect a partial sintering of the mixture. This is done by heating the mass at 350 to 600 C. fora period of 3 to 10 hours. The use of temperatures in the upper part of the range or the use of longer heating times give a physically-stronger but less active catalytic mass. Preferably the silver-beryllum oxide mixture is heated at 400 to 500 C.

such as copper, aluminum, manganese, cobalt,-

iron, magnesium, gold, thorium, nickel, cadmium, cerium and zinc. These promoters may be used singly or in combination and may be incorporated with the silver-beryllium oxide catalyst in any suitable manner such as by mechanical mixture or coprecipitation.

While the silver-beryllium catalytic mixtures of the invention may be advantageously employed for some purposes without resorting to the use of a support or carrier, it is preferred, particularly for use in fluid-flow processes, that the catalytic mixtures be deposited upon a divided granular solid support or carrier. There may be employed any of the various materials suggested in the art as supports, carriers, or diluents such as firebrick, alumina, corundum, alundum, pumice, silica gel, calcined diatomaceous earth, zeolites or other aluminum silicates such as analcite, natrolite and nephelite.

The metallic silver-beryllium oxide containing catalytic mixture may be applied to thecarrier or support and made, adherent'thereto or dispersed thereon in any of the manners previously employed in the preparation of silver catalysts; If desired, the mixture of the coprecipitate and the freshly prepared reducible silver compounds may be applied to the support and the resulting mixture may either thermally or chemically be reduced in order to present the metallic silver beryllium oxide mixture on the carrier as an active catalyst. V

The amount of silver present in the dispersion of the silver-beryllium oxide containing catalytic material on or in a carrier may be varied,but it will ordinarilybe found most economic to use from 30 'to 500 grams of silver per liter of total catalyst'composition, and still more'preferably from '75 to 200 grams of silver per liter of total catalyst composition.

The selection of the particle size of the support or carrier will ordinarily follow the design of a specific process and apparatus. For use in fluid-flow processes for the oxidation of ethylene, for which the catalyst compositions of this invention are particularly well-suited, the carrier should have a particle size less than about 35 mesh. After'a gas velocity :has been selected, the specific particle size can'be adjusted so that the catalyst composition canbe suspended by the gas stream. 7 Y l In addition to the catalytic. 'silver beryllium oxide mixture, and the carrier or support,.the total catalyst compositionsof the invention may include other materials such as the conventional promoters and diluents, and also conditioning agents. v

The following examples illustrate catalytic compositions of the invention, methods by which they are prepared and processes for their use.

Example I This example shows the preparation and use of a silver catalyst composition of the invention in.

5 pound is admixed therewith in amount corresponding to 50 parts byweight of silver for each partby weight of beryllium in the coprecipitate to give a resulting mixture having a Ag:Be weight ratio of 200 t 1.

A solution of 59.1 g. silver nitrate and 5.2 g. beryllium nitrate trihydrate in one liter of'water' is mixed with a solution of 17 g. sodium hydroxide in 153 cc. water by rapid addition of the alkali with good stirring. After stirring ten minutes to insure homogeneity, formed is Washed five times :by allowing to settle, decanting the water, and adding an equal volume of fresh distilled water. T i

After the final wash-, the precipitate suspended inasmall amount of remaining water is mixed with a slurry prepared as follows: v

19.7 g. silver nitrate-is dissolved in 500 cc. water and precipitated with a solution of 5 g. sodium hydroxide in 45 cc. water. This suspension is washed in the same manner as the silver oxidehydrated beryllium oxide prepared above and then is added to that; mixture as indicated.

The resulting slurry is stirred. rapidly for minutes in one liter of water and then allowed to settle. The supernatant liquid is decanted and the precipitate is filtered almost to dryness using a vacuum filter. The solids are reslurried four times with 100 cc. pure acetone, then sucked dry as possible on a vacuum filter and then heated for four hours at 65 C. The dried oxide mixture is ground to pass a 48 mesh screen.

20.4 g. of the dried oxide mixture prepared as above is stirred in acetone slurry with 37 g. calcined diatomaceous earth (sized 80-200 mesh) until dry enough to be free flowing. It is then dried in a stream of nitrogen, first at room temperature and then at a temperature of about 175 C. When dried, the resulting supported oxide mixture is reduced by passing a stream of 2% ethylene in nitrogen thru a fixed bed of material at 175 C. to give a supported silver-beryllium oxide composition.

The supported silver-beryllium oxide composition is then heated in air at 400 C. for five hours. After cooling it is then diluted with twice its volume of granular artificial graphite (sized 80-200 mesh) to give a finished catalyst composition.

Using the catalyst composition of this example in a boiling-bed type operation with a feed gas containing 10% ethylene in air, a temperature of 260-280 (3., a gas space velocity of 1800 hr. and a linear gas velocity of 0.5 ft. per second, 44% of the ethylene reacts, and 61% of the reacted ethylene forms ethylene oxide.

The feature of conditioning silver-containing catalysts with granular artificial graphite, a specific application which is shown in the above example, is claimed in coassigned copending Sears application, Serial No. 100,982, filed June 23, 1949.

Example II In this example the AgzBe weight ratio in the coprecipitate is 67:1 and the separately prepared silver compound is added thereto in amount corresponding to 33 parts by weight of silver for each part by weight of beryllium in the coprepitate,

thus giving a mixture having a AgzBe weight ratio of 100:1.

A preparation of the composition'of this example differs from that of the composition of Example I in the following respects: 52.5 g. silver nitrate and 10.4 g. beryllium nitrate trihydrate are used in the coprecipitation step; and 26.3 g.

the precipitate which silver-nitrate and 6.5. g. sodium hydroxide: are

used in separately preparing reducible: oxygen.- containing silver compound. The heat treatment. of the reduced silver-beryllium oxide mixture was carried out at 500 C. for four hours.

Operating an ethylene oxidation process with. the catalyst. composition of this example. at'a temperature of. 270-290 0.. and the remaining conditions as in Example I, 41% of the ethylene reacts and 60% of the reacted ethylene forms ethylene oxide.

Example III A- catalyst. compositionv is prepared according, to the general process described in Example I except that the amounts of reagents are varied to give a coprecipitate having an AgzBe weight. ratio of 100:1 and this is intimately mixed with a separately prepared silver oxide, the silver oxide being, used in amountrcorres'ponding to 100 parts 1 by weight of silver for each part by weight of beryllium in the coprecipitate to give a resulting mixture having a AgrBe weight ratio of 200:1.

Operating the composition of this example in ethylene oxidation process at a temperature of 280-310 C. and other conditions as in Example I, 38%" of the ethylene reacts and 59% of the reacted ethylene forms ethylene oxide, as an average; over 35 hours of operation.

Example IV A catalyst composition is prepared in essentially the same manner as Example I except for the following changes.

23.6 g. silver nitrate and 6.2 beryllium nitrate trihydrate are precipitated with 10 g. sodium hydroxide in cc. of water in the coprecipitation step; and 55.2 g. silver nitrate are precipitated with 14 g. sodium hydroxide in 126 cc. of water in making the separate corporation of reducible silver compound. Thus the coprecipitate is formed having a AgzBe weight ratio of 50:1 and to this there is added a reducible silver compound in amount corresponding to 116 parts by weight of silver for each part of beryllium in the coprecipitate to give a resulting mixture having a Ag:Be weight ratio of 166: 1.

The catalyst composition of this example operated in a boiling-bed process at a temperature of 1 280-300" C. using a feed of 10% ethylene in air at a space velocity of 1800 hr.- and a linear velocity of 0.5 ft./sec., causes 36% of the ethylene fed to react, and 63% of the reacted ethylene forms ethylene oxide, as an average, over 200 hours of operation.

We claim:

1. A process for preparing a silver-beryllium oxide catalyst adapted to catalyze the oxidation of ethylene to ethylene oxide which comprises coprecipitating a reducible oxygen-containing compound of silver and a corresponding compound of beryllium in a silver:beryllium weight ratio of from 5:1 to 150:1 from a solution of a silver compound and a beryllium compound, intimately mixing said coprecipitate with a separately prepared reducible oxygen-containing compound of silver, said separately prepared silver compound being added in the mixing step in amount corresponding to at least 25 parts by weight of silver for each part by weight of beryllium in the coprecipitate and in amount sufficient to give a resulting mixture in which the Ag:Be weight ratio is in the range of :1 to 500:1; then reducing the intimate mixture to a mixture of metallic silver and beryllium oxide and heating the reduced mixture at about 350 to 600 C. for 3 to 10 hours.

2. A catalyst composition adapted'to catalyze the oxidation of ethylene to ethylene oxide which comprisesas an active catalytic material a silverberyllium oxide mixture obtained by coprecipitating a reducible oxygen-containing compound of silver and a corresponding compound of beryllium in a silver:beryllium weight ratio of from 5 :1 to 150: 1 from a solution of a silver compound and a beryllium compound, intimately mixingv said coprecipitate with a separately prepared reducible oxygen-containing compound of silver, said separately prepared silver compound being added in the mixing step in amount corresponding to at least 25 parts by weight of silver for each part by weight of beryllium in the coprecipitate and in amount sufficient to give a resulting mixture in which the Ag: 3e weight ratio is in the range of 100:1 to 500:1; then reducing the intimate mixture to a mixture of metallic silver and beryllium oxide and "heating the reduced mixture at about 350 to 600 C. for-3to hours.

3. A catalyst composition adapted to catalyze the oxidation of ethylene to ethylene oxide which comprises a divided granular carrier and dispersed thereon as an active catalytic material a silver:beryllium oxide mixture, the silver constituting from 75 to 200 grams per liter of total catalyst composition, and the silver-beryllium oxide mixture being obtained by coprecipitating a reducible oxygen-containing compound of silver and a corresponding compound of beryllium in a silverzberyllium weight ratio of 5:1 to 150:1 from an aqueous solution of the nitrates of said metals, intimately mixing said coprecipitate in liquid suspension with a separately prepared reducible oxygen-containing compound of silver, said separately prepared silver compound being added in the mixing step in amount corresponding toat least 25 parts by weight of silver for each'part by weight of beryllium in the coprecipitate and in amount suificient to give a resulting mixture in which the AgzBe weight ratio is in the range of :1 to 500:1; then reducing the intimate mixture to a mixture of metallic silver and beryllium oxide and then heating the reduced mixture at 400 to 500 C. for 4 to 5 hours.

GEORGE W. SEARS, JR. WALLACE W. THOMPSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,354,892 Thacker Aug. 1, 1944 2,554,459 Heider May 22, 1951 

1. A PROCESS FOR PREPARING A SILVER-BERYLLIUM OXIDE CATALYST ADAPTED TO CATALYZE THE OXIDATION OF ETHYLENE TO ETHYLENE OXIDE WHICH COMPRISES COPRECIPITATING A REDUCIBLE OXYGEN-CONTAINING COMPOUND OF SILVER AND A CORRESPONDING COMPOUND OF BERYLLIUM IN A SILVER: BERYLLIUM WEIGHT RATIO OF FROM 5:1 TO 150:1 FROM A SOLUTION OF A SILVER COMPOUND AND A BERYLLIUM COMPOUND, INTIMATELY MIXING SAID COPRECIPITATE WITH A SEPARATELY PREPARED REDUCIBLE OXYGEN-CONTAINING COMPOUND OF SILVER, AND SEPARATLY PREPARED SILVER COMPOUND BEING ADDED IN THE MIXING STEP IN AMOUNT CORRESPONDING TO AT LEAST 25 PARTS BY WEIGHT OF SILVER FOR EACH PART BY WEIGHT OF BERYLLIUM IN THE COPRECIPITATE AND IN AMOUNT SUFFICIENT TO GIVE A RESULTING MIXTURE IN WHICH THE AG:BE WEIGHT RATIO IS IN THE RANGE OF 100:1 TO 500:1, THEN REDUCING THE INTIMATE MIXTURE TO A MIXTURE OF METALLIC SILVER AND BERYLLIUM OXIDE AND HEATING THE REDUCED MIXTURE AT ABOUT 350 TO 600* C. FOR 3 TO 10 HOURS. 